Editing PNG (section)

== History and development ==
{{See also|Graphics Interchange Format#Unisys and LZW patent enforcement}}

The motivation for creating the PNG format was the announcement on 28 December 1994 that implementations of the [[Graphics Interchange Format]] (GIF) format would have to pay royalties to [[Unisys]] due to their [[patent]] of the [[Lempel–Ziv–Welch]] (LZW) [[data compression]] algorithm used in GIF.<ref>{{Cite web |title=Offical{{sic |nolink=yes}} Compu$erve announcement about GIF licensing |url=https://groups.google.com/g/comp.infosystems.www.users/c/NTgvxli1oxI/m/y9K0X9xicioJ |access-date=2025-01-08 |website=groups.google.com}}</ref> This led to a flurry of criticism from [[Usenet]] users. One of them was Thomas Boutell, who on 4 January 1995 posted a precursory discussion thread on the [[Usenet newsgroup]] "comp.graphics" in which he devised a plan for a free alternative to GIF. Other users in that thread put forth many propositions that would later be part of the final file format. Oliver Fromme, author of the popular [[JPEG]] viewer [[QPEG]], proposed the PING name, eventually becoming PNG, a [[recursive acronym]] meaning ''PING is not GIF'',<ref>{{cite news |last=Limer |first=Eric |url=https://www.popularmechanics.com/technology/a21457/the-gif-is-dead-long-live-the-gif/ |title=The GIF Is Dead. Long Live the GIF. |work=Popular Mechanics |date=2019-10-30 |accessdate=2022-11-21 |url-access=subscription}}</ref> and also the .png [[Filename extension|extension]]. Other suggestions later implemented included the [[Deflate|deflate compression algorithm]] and [[Color depth#True color (24-bit)|24-bit color]] support, the lack of the latter in GIF also motivating the team to create their file format. The group would become known as the PNG Development Group, and as the discussion rapidly expanded, it later used a mailing list associated with a [[CompuServe]] forum.<ref name="pnghist"/>{{Sfn|Roelofs|1999|loc=Chapter 7. History of the Portable Network Graphics Format}}

The full specification of PNG was released under the approval of [[World Wide Web Consortium|W3C]] on 1 October 1996, and later as [[Request for Comments|RFC]] 2083 on 15 January 1997. The specification was revised on 31 December 1998 as version 1.1, which addressed technical problems for [[gamma correction|gamma]] and [[color correction]]. Version 1.2, released on 11 August 1999, added the iTXt chunk as the specification's only change, and a reformatted version of 1.2 was released as a second edition of the W3C standard on 10 November 2003,<ref name="w3IHDR"/> and as an International Standard ([http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=29581&scopelist=PROGRAMME ISO/IEC 15948:2004]) on 3 March 2004.<ref>{{cite web|url=http://libpng.org/pub/png/spec/|title=Portable Network Graphics (PNG) Specification and Extensions|last=Roelofs|first=Greg|work=[[libpng]]|date=29 September 2011|access-date=August 15, 2021}}</ref><ref name="iso" />

Although GIF allows for [[computer animation|animation]], it was initially decided that PNG should be a single-image format.{{ref RFC |2083|section=8.4 |quote=PNG itself is strictly a single-image format. (...) In the future, a multiple-image format based on PNG may be defined. Such a format will be considered a separate file format}} In 2001, the developers of PNG published the [[Multiple-image Network Graphics]] (MNG) format, with support for animation. MNG achieved moderate application support, but not enough among mainstream web browsers and no usage among web site designers or publishers. In 2008, certain [[Mozilla]] developers published the [[Animated Portable Network Graphics]] (APNG) format with similar goals. APNG is a format that is natively supported by [[Gecko (software)|Gecko]]- and [[Presto (browser engine)|Presto]]-based web browsers and is also commonly used for thumbnails on Sony's [[PlayStation Portable]] system (using the normal PNG file extension). In 2017, Chromium based browsers adopted APNG support. In January 2020, [[Microsoft Edge]] became [[Chromium (web browser)|Chromium]] based, thus inheriting support for APNG. With this all major browsers now support APNG.